In the following years, Joule expanded on his work, via more precise experiments, and published the definitive form of his "On the Mechanical Equivalent of Heat", in nineteen pages, in the transactions of the Philosophical Society of London. [2]

References1. Joule, James P. (1845). "On the Mechanical Equivalent of Heat", Brit. Assoc. Rep., trans. Chemical Sect, p.31, read before the British Association at Cambridge, June. 2. (a) Joule, James P. (1847). “On the Mechanical Equivalent of Heat: as Determined by the Heat evolved by the Friction of Fluids.” Phil. Mag. Vol. 31, pg. 173-78. Read before the Mathematical and Physical Section of the British Association at Oxford, June. (b) Joule, James P. (1850). “On the Mechanical Equivalent of Heat.” Philosophical Transactions of the Royal Society of London, 140: 61-82.